Did Gideon do anything specifically bad? I agree underperforming Biden by 20 points is a huge shock, but did she do something wrong or is Collin's brand strength bigger than we thought?
I think on reflection there's a difference between a bad candidate and a bad campaign; she was on paper quite a weak candidate (had never won a state wide or competitive office, first big campaign, was a career politician etc) & the attacks seemed based on things she couldn't change- a lack of experience, not being from Maine etc.
If someone said that Steve Bullock and Sara Gideon ran some of the worst campaigns on November 2nd, 2020, I think they would be laughed at and mocked. There are legitimate arguments to be had, but you can run a good campaign that doesn't end up with a favorable result. Those campaigns got nothing but praise from the mainstream media and people on here until they didn't get the result they wanted.
IIRC there were a few democrats quoted in articles saying they were worried that Gideon had failed to 'put the race away'; my perception of the race was that she was running a standard nationalised campaign race which assumed a much better national election result